The US National Transportation Safety Bureau( NTSB) has identified the origin of a fire aboard a JAL 787 at Boston Airport as being the aircraft’s battery.
NTSB chairman Deborah Hersman said: “After an exhaustive examination of the JAL lithium-ion battery, which was comprised of eight individual cells, investigators determined that the majority of evidence from the flight data recorder and both thermal and mechanical damage pointed to an initiating event in a single cell. That cell showed multiple signs of short circuiting, leading to a thermal runaway condition, which then cascaded to other cells. Charred battery components indicated that the temperature inside the battery case exceeded 260C.”
Hersman added that potential causes of the initiating short circuit currently being evaluated include battery charging, the design and construction of the battery, and the possibility of defects introduced during the manufacturing process.
Investigations will now centre on the design and certification requirements for the battery, the latter aspects heightening concern at the methodology used by the US Federal Aviation Administration (FAA) to conditionally approve the use of the lithium-ion batteries onboard the aircraft.
“During the 787 certification process, Boeing studied possible failures that could occur within the battery,” Hersman said. “Those assessments included the likelihood of particular types of failures occurring, as well as the effects they could have on the battery. In tests to validate these assessments, Boeing found no evidence of cell-to-cell propagation or fire, both of which occurred in the JAL event.”
To support further testing, the FAA recently approved strictly-controlled crew-only 787 flights.
The NTSB is expected to release an interim report by mid-March, with the likelihood growing of the worldwide 787 fleet not returning to commercial service until at least April.